Endodontic therapy is a sequence of treatment for the pulp of a tooth which results in the elimination of infection and protection of the decontaminated tooth from future microbial invasion. This set of procedures is commonly referred to as a “root canal.” Root canals and their associated pulp chamber are the physical hollows within a tooth that are naturally inhabited by nerve tissue, blood vessels and other cellular entities. Endodontic therapy involves the removal of these structures, the subsequent cleaning, shaping, and decontamination of the hollows with tiny files and irrigating solutions, and the obturation (filling) of the decontaminated canals with an inert filling such as gutta percha and typically a eugenol-based cement. After endodontic surgery the tooth will be “dead,” and if an infection is spread at apex, root end surgery is required.
In the situation that a tooth is considered so threatened (because of decay, cracking, etc.) that future infection is considered likely or inevitable, a pulpectomy, removal of the pulp tissue, is advisable to prevent such infection. Usually, some inflammation and/or infection is already present within or below the tooth. To cure the infection and save the tooth, the dentist drills into the pulp chamber and removes the infected pulp and then drills the nerve out of the root canal(s) with long needle-shaped drills. The dentist then cleans and shapes (debrides) the canal using a file. The canal is then irrigated thoroughly, using a bleach solution. After this is done, the dentist fills each of the root canals and the chamber with an inert material, typically gutta percha, and seals up the opening. With the removal of nerves and blood supply from the tooth, it is best that the tooth be fitted with a crown which improves the prognosis of the tooth.
A successful procedure (one that does not require retreatment) depends in large part on how thoroughly the canals are debrided and irrigated prior to filling. During canal preparation, the file debrides the canal of larger materials, and the sodium hypochlorite solution helps digest and remove pulp and bacteria, viruses, spores, endotoxins and other irritants generated by the microorganisms in the canal system. However, studies have shown that even the most thorough use of sodium hypochlorite does not remove all the material from the root canals. The walls of a root canal are comprised of dentin which contains millions of dentinal tubules per square millimeter, and the irritants can find their way into the tubules of the root canal systems. Thus, after cleaning and shaping procedures, the root canal is still covered with a film of debris, frequently described in the literature as a “smear layer.” This “smear layer” includes dentinal mud and/or organic debris. This smear layer is generally not removed by the action of a file, because the file does not have the requisite flexibility in terms of its shape, to thoroughly clean the walls of the canal, and remove the smear layer from the walls. In addition, endodontic files are usually round along the length, while pulp canals are ovoid. Because of this, many areas of the canal are mechanically untouched by the file. The “smear layer” can include microorganisms that may reinfect the tooth, thereby requiring retreatment.